linux-kernel - Re: [PATCH] xhci-hub.c: handle command

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Date:	Wed, 9 Oct 2013 13:18:46 -0700
From:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
To:	Xiao Jin <jin.xiao@...el.com>
Cc:	gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	mingo@...e.hu, a.p.zijlstra@...llo.nl, rusty@...tcorp.com.au,
	william.douglas@...el.com, sboyd@...eaurora.org, jslaby@...e.cz
Subject: Re: [PATCH] xhci-hub.c: handle command_trb that may be link TRB

Hi Xiao,

Thanks for taking the time to submit this patch.  Comments below.

On Wed, Oct 09, 2013 at 09:42:36AM +0800, Xiao Jin wrote:
> From: xiao jin <jin.xiao@...el.com>
> Date: Wed, 9 Oct 2013 09:38:45 +0800
> Subject: [PATCH] xhci-hub.c: handle command_trb that may be link TRB

I won't be able to apply your patch  because it has these extra lines in
the body ^^^.  I suspect you used `git format-patch` to produce this,
and then tried to copy-paste it into your mail client?  You can't do
that, because your mail client will probably word-wrap your patch, and
possibly turn tabs into spaces.  You need to use `git send-email`
instead to send your patches.

> When xhci stop device, it's possible cmd_ring enqueue point to
> link TRB after queue the last but one stop endpoint. We must
> handle the command_trb point to the next segment trb. Otherwise
> xhci stop devie will timeout because command_trb can't match
> with cmd_ring dequeue.
> 
> The patch is to let command_trb point to the next segment trb if
> cmd_ring enqueue point to link TRB.
> 
> Signed-off-by: xiao jin <jin.xiao@...el.com>
> ---
>  drivers/usb/host/xhci-hub.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/usb/host/xhci-hub.c b/drivers/usb/host/xhci-hub.c
> index 1d35459..4872640 100644
> --- a/drivers/usb/host/xhci-hub.c
> +++ b/drivers/usb/host/xhci-hub.c
> @@ -287,6 +287,13 @@ static int xhci_stop_device(struct xhci_hcd *xhci, int slot_id, int suspend)
>  			xhci_queue_stop_endpoint(xhci, slot_id, i, suspend);
>  	}
>  	cmd->command_trb = xhci->cmd_ring->enqueue;
> +	/* Enqueue pointer can be left pointing to the link TRB,
> +	 * we must handle that
> +	 */
> +	if (TRB_TYPE_LINK_LE32(cmd->command_trb->link.control))
> +		cmd->command_trb =
> +			xhci->cmd_ring->enq_seg->next->trbs;
> +
>  	list_add_tail(&cmd->cmd_list, &virt_dev->cmd_list);
>  	xhci_queue_stop_endpoint(xhci, slot_id, 0, suspend);
>  	xhci_ring_cmd_db(xhci);

What kernel version or tree is it against?  I ask because there's
already a fix in the 3.12-rc4 kernel for this:

static int xhci_stop_device(struct xhci_hcd *xhci, int slot_id, int suspend)
{
...
        spin_lock_irqsave(&xhci->lock, flags);
        for (i = LAST_EP_INDEX; i > 0; i--) {
                if (virt_dev->eps[i].ring && virt_dev->eps[i].ring->dequeue)
                        xhci_queue_stop_endpoint(xhci, slot_id, i, suspend);
        }
        cmd->command_trb = xhci_find_next_enqueue(xhci->cmd_ring);
...

Where xhci_find_next_enqueue is defined as:

union xhci_trb *xhci_find_next_enqueue(struct xhci_ring *ring)
{
        /* Enqueue pointer can be left pointing to the link TRB,
         * we must handle that
         */
        if (TRB_TYPE_LINK_LE32(ring->enqueue->link.control))
                return ring->enq_seg->next->trbs;
        return ring->enqueue;
}

That was added in commit ec7e43e2d98173483866fe2e4e690143626b659c "xhci:
Ensure a command structure points to the correct trb on the command
ring"  It's in (or should be in soon) the stable kernels as well.

Sarah Sharp
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